Made a PCV holder for my new valve covers. Pretty sweet if I say so myself!

Mopar to ya said
1 1/4", but technically 1.22" I'm trying to find a way to do a breather on the other side with the same cap.

Damn, Im still trying to find a 1-1/2" grommet or cap that has the thicker surface area like that cap does.

The breather might be tough, with how large the hole typically is on those. Good luck and let us know if you do come up with an idea.